Masterthesis: Ab Initio Magnetic Properties of Rare-Earth Lean Nd-based Hard Magnets

Stephan Erdmann

paper

Masterthesis: Ab Initio Magnetic Properties of Rare-Earth Lean Nd-based Hard Magnets

arXiv:2302.03417

Abstract

Due to the resource criticality of rare-earths (RE), an alternative to the well-known Nd $_{2}$ Fe $_{14}$ B magnets with a lower amount of critical elements is required. In this work, density functional theory (DFT) calculations to investigate the influence of partial Nd substitution with more abundant elements (X: Y and Ce) in ThMn $_{12}$ -type (Nd,X)Fe $_{11}$ Ti compounds were performed. In order to have a systematic understanding, the intrinsic magnetic properties such as the saturation magnetization $M_{S}$ , Curie temperature $T_{C}$ and magnetocrystalline anisotropy energy, are screened starting from binaries RFe $_{12}$ (R: Y, Ce and Nd), and only considering the spin magnetic contribution in case of the $f$ electrons. Ti is considered for the thermodynamic stabilization and different concentrations of Ti are taken into account for ternaries RFe $_{12 - y}$ Ti $_{y}$ and quaternaries (Nd,X)Fe $_{12 - y}$ Ti $_{y}$ (0.5 $\leq$ $y$ $\leq$ 1). In addition, the effect of nitrogenation is examined for each considered compound. In case of (Nd,Y)Fe $_{11}$ Ti, $∣ B H ∣$ $_{ma x}$ is found to be 384 kJ/m $^{3}$ and $T_{C}$ is calculated to be 595 K. Similarly, $∣ B H ∣$ $_{ma x}$ and $T_{C}$ are calculated to be 365 kJ/m $^{3}$ and 593 K for (Nd,Ce)Fe $_{11}$ Ti magnet, respectively. Both 50 % Nd-lean magnets exhibit higher $∣ B H ∣$ $_{ma x}$ compared to Sm $_{2}$ Co $_{17}$ and $T_{C}$ than Nd $_{2}$ Fe $_{14}$ B. For both cases, the theoretical magnetic hardness factor $κ$ is calculated to be 1.20, which qualifies them as good candidates for RE-lean permanent magnets.